OF SOUND AND HEARING. 227 



to be made with alacrity, but by the air and other environing 

 adversaries presently to be destroyed. 



The whistling, which is made by the mouth without use 

 of a whistle, may be effected by sucking in of the breath 

 toward the inner parts of the mouth, not only by expelling 

 of the breath outwards; and clearly all sucking of the air 

 inwards gives a sound, which seems exceeding worthy of 

 remark : because the sound is generated against the per 

 ceptible motion of the air, so as the first impulsion of the 

 air appears plainly to be the remote efficient and no part 

 of the form of sound. 



In like manner, if there be an egg of glass taken, and 

 the air through a small hole forcibly sucked out; then the 

 hole stopped with wax, and it be laid by for a time; if 

 afterwards the wax be removed from the hole, you shall 

 hear plainly the hissing of the air entering into the egg, 

 being drawn to wit by the inner air, after forcible rarefac 

 tion, restoring itself. So as in this trial also, sound is 

 generated contrarily to the perceptible motion of the air. 



In like manner, in the toy that is called a jew s-harp, 

 holding the sides betwixt the teeth, the little tongue of 

 iron is drawn outwards and jarred, when it flies back 

 inwards against the air that is in the mouth, and thence is 

 a sound created. 



And in these three trials it may not be doubted but that 

 sound is generated by the percussion of the air inwards 

 towards the mouth on the egg of glass. 



Sound is generated by percussions. The percussion is 

 either of air against air, or of an hard body against the air, 

 or of an hard body against an hard body. 



The instance of the percussion of air against air chiefly 

 prevails in the human voice, and in the voices of birds and 

 of other animals ; next in musical wind instruments ; also 

 in ordnance, greater and less, where the percussion that 

 gives the sound is generated chiefly by the percussion of 

 the confined air that issues from the mouth of the piece 

 against the outer air ; for the bullet wherewith it is charged 

 makes not much to the noise. Neither is the percussion 

 of a soft body against a soft body only seen in the percus 

 sion of air against air, but also of air against flame, as in 

 the raising of a flame with bellows ; also flames amongst 

 themselves, when one drives another, yield a certain roaring; 

 but whether the air assist here may be further inquired. 

 Also, all flame that suddenly taketh, if it be of any great 

 ness, makes a sound, rather as I think in displacing of the 



